(Rewrites throughout, adds details about interim results)
SYDNEY, July 29 (Reuters) - QBE Insurance Group, Australia's biggest insurer by premium income, on Tuesday warned that its first-half results would likely fall short of analysts' forecasts, hit by higher-than-expected claims.
QBE said it expected insurance profit margin at 7 percent to 8 percent compared with consensus expectations of about 10 percent. Operating ratio - operating expenses as a percentage of revenue - would likely be 96 percent to 97 percent against consensus expectations of around 93 percent.
Net profit after tax would be A$390 million ($367.03 million), it added. That compares with a consensus forecast of A$571.8 million, according to Thomson Reuters Starmine data.
The announcement sent QBE shares plunging 12.11 percent to A$10.45 in early trades, compared with a 0.19 percent dip on the benchmark S&P/ASX200 index.
Higher claims in Argentina, crop damage in Latin America, UK floods and storms in North American and Europe offset benign catastrophe claims in Australia, QBE said in a statement.
In contrast, QBE's arch rival Insurance Australia Group has raised its profit margin guidance for 2014 from as low as 14.5 percent to up to 18.3 percent on lower disaster claims in Australia.
IAG will announce full year-results on Aug. 19, the same day QBE will post its interim results.
The Sydney-based firm is in the process of cutting costs in North America as well as improving its loss-making lender-placed insurance business, it added.
Gross written premiums of around A$8.5 billion for the half had come in below its budget of A$8.9 billion.
The group is facing a class action lawsuit from shareholders over its profit downgrade for fiscal-year 2013, which sent QBE shares plunging over 20 percent on Dec. 9, wiping A$4 billion off the company's market value.
QBE posted an annual net loss of $254 million in February.
$1 = 1.0626 Australian Dollars Reporting by Swati Pandey; Editing by Stephen Coates